Your question answer is here
a. Solution ,
Given volume (V)=30cm^3
Mass = 180 g
Density =?
We know that,
Density = given mass/volume
Or. 180/30
=6g/cm^3
b. We know ,
If any pice of stone have equal density so each piece have 6g/cm^3
c. We know ,
Given weight = 80g
Density = 6g/cm^3
Volume =?
We know that,
Volume = given weight ( mass)/ density
= 80/6
= 13.33 cm^3